1. Field of the Invention
The present invention is concerned with the recovery of stevioside from the Stevia rebaudiana Bert. Hemsl. (Compositae), hereinafter referred to as Stevia rebaudiana. More particularly, the invention pertains to an improved method for recovery of stevioside from the Stevia rebaudiana plant without the need to use chemicals that might in turn end up as undesirable impurities in the stevioside product or which require the use of equipment that render commercial operations uneconomic.
Stevioside of a natural origin is gaining favor as a low calorie or nutritive sweetener. It has been used commercially in Japan for many years and recently in Brazil to sweeten a variety of foods. The present investigation was undertaken in order to find a commercially viable method for the isolation of purified stevioside, since it is present only to an extent of 8-10% in the Stevia rebaudiana leaves.
Stevioside is one of the eight known sweet ent-kaurene glycoside constituents of Stevia rebaudiana; the others being Steviolbioside, rebaudicides A-E, and dulcoside-A. Stevioside possesses the empirical formula C.sub.36 H.sub.60 O.sub.18 and the following structural formula: ##STR1##
2. Description of the Prior Art
U.S. Pat. No. 4,361,697 which issued on Nov. 30, 1982 to Dobberstein and Ahmed discloses a process for the recovery of diterpene glycosides, including stevioside from the Stevia rebaudiana plant. A variety of solvents, having different polarities, were used in a sequential treatment that concluded with a high performance liquid chromatographic (HPLC) separation procedure.
Dobberstein and Ahmed called attention to U.S. Pat. No. 4,082,858 which issued on Apr. 4, 1979 to Morita et al. This earlier patent is directed to the recovery of rebaudside A from the leaves of Stevia rebaudiana plants. Again, final purification is achieved by liquid chromatography subsequent followed by an initial extraction with water an alkanol having from 1 to 3 carbon carbons, preferably methanol. Although Dobberstein and Ahmed also disclose that water may be used as the initial solvent, their preferred solvent at this stage is a liquid haloalkane having from 1 to 4 carbon atoms. The preferred second solvent is an alkanol having from 1 to 3 carbon atoms, while the preferred third solvent is an alkanol having from 1 to 4 carbon atoms and optionally minor amounts of water.
In addition to Morrita et al. the Dobberstein and Ahmed patent shows the following list of cited U.S. patent references:
U.S. Pat. No. 3,723,410, Persinos PA1 U.S. Pat. No. 4,109,075, Deaton PA1 U.S. Pat. No. 4,171,430, Matsushita et al. PA1 U.S. Pat. No. 4,256,876, Gabriel et al.
Publications cited include two articles by Y. Hashiomoto et al. and one article by M. S. Ahmed et al.
There are also numerous published Japanese patent applications, only abstracts of which are available, which deal with the separation of steviocide from naturally occurring sources. Some of the more relevant Japanese patents with respect to the present invention are set forth below:
______________________________________ Toyo Sugar Refining 57198 May 1977 Chigai Pharmaceutical 51069 April 1977 Ajinomoto 62300 May 1977 Sanei Chem. Ind. 148574 Dec. 1978 Sanei Chem. Ind. 148575 Dec. 1978 Sanyo Kokusaku Pulp 132599 Oct. 1979 Teijin Eng. 21752 Feb. 1980 Seisan Kaihatsu 39731 March 1980 Seisan Kaihatsu 81567 June 1980 Oshiro Chiyi Sholten 92323 July 1980 Ajinomoto 121454 Sept. 1981 Dick Fine Chem. 160962 Dec. 1981 Maruzen Kasei 86264 May 1982 Shin-Nakamura 42300 Sept. 1982 Matsubishi Acetate 28247 Feb. 1983 Sekisui Chem. Ind. 212759 Dec. 1983 ______________________________________
It is abundantly clear from the above patent literature that there have been numerous proposals for the recovery and separation of stevioside from Stevia rebaudiana plants. The proposals have included treatments such as ion-exchange, column chromatography, multiple solvent extractions, etc. In many of these processes undesirable chemicals have to be employed or the equipment required is too expensive for practical commercial operations.
It is therefore a principal object of the present invention to provide an improved method for the treatment of Stevia rebaudiana plants to recover purified stevioside therefrom utilizing innocuous chemicals in the separation procedures; while eliminating the need for large volumes of solvents as well as the use of expensive ion exchange resins, chromatographic equipment, and the like.